Hygrometer



July 3, 1934. F FOSTER 1,965,309

HYGROMETER Filed June 2, 1933 4 Sheets-Sheet 1 INVENTOR ATTORNEY F. B. FOSTER HYGROMETER July 3, 1934.

Filed June 2, 1955' 4 Sheets-Sheet 2 Rana/'65! x aszer ATTOR N EY y 1934- F. B. FOSTER 1,965,309

HYGROMETER Filed June 2, 1933 4 Sheets-Sheet 5 mam/6525; BY A86: M

ATTORN EY July 3, 1934.

F. B. FOSTER HYGBOMETER Filed June 2, 1933 g She etS-Sheet 4 whyzm zz Patented July 3, 1934 HYGROMETER Francis B. Foster, Milton, Mass. Application June 2, 1933, Serial No.]674,064

2 Claims.

This invention relates to hygrometers employing dry and wet bulb thermometers and has for its object the provision of means whereby the relative humidity may be indicated directly by the action of the thermometric elements.

Another object of the invention is to provide positively acting indicating means of simple construction which will be responsive/to the dry and wet bulb thermometers simultaneously so that an Figure 3 is a side elevation looking in the opposite direction from that assumed in Figure '2.

Figure 4 is a plan view showing a different form of mechanism.

Figure 5 is a side elevation of the mechanism shown in Figure 4.

Figure 6 is an end elevation of the same.

Figures '7 and 8 are diagrams.

In the drawings, the reference numeral 1 indicates a dry bulb thermometer and the numeral 2 indicates a wet bulb thermometer which may be ofany approved form. In the mechanism shown in the accompanying drawings there is provided a cam 3 which is mounted upon a shaft 4 so as to slide upon the shaft but be incapable of rotating independently of the shaft, the shaft being non-circular in cross section, and the bore of the cam hub being of the same contour. It will be understood, however, that the cam may be feathered'upon the shaft, if preferred, or any other mounting employed which will permit the sliding movement of the cam but prevent independent rotation thereof. The shaft 4 is mounted in suitable bearings 5 which may be provided upon posts or studs '6 or otherwise supported. The dry bulb thermometer 1 is connected at one end directly with a capillary tube '1 which extends to a Bourdon tube 8 which is disposed about the shaft 4 and is normally concentric therewith. One end of the Bourdon tube is, of course, fixed at. its connection with the capillary tube '7 but the opposite 'end of the tube is connected by a link 9 with an arm 10 disposed radially of its pivotal support 11 upon a post 12, and disposed concentric with the pivot 11 is a segmental rack 13 which in turn meshes with a gear 14 fixed upon the end of the shaft 4; It will thus be seen that as the temperature of the dry bulb thermometer and the mercury therein rises the mercury in said thermometer will beforced through the tube '7 and the Bourdon tube and the latter will tend to straighten so that its free end will exert a pull upon the link 9 which will rock the segmental gear 13 and rock the shaft 4 in a corresponding degree so that the cam 3 will be turned through apart of a circle. This cam is semicircular in extent and its body is given a somewhat helical formation, the exact shape of the cam or degree of curvature of the helical surfaces being determined by the use of the charts shown in Figures '7 and 8. These charts may be developed from a series of experiments or may be developed from data which has been accepted as standard. The degrees of relative humidity are marked upon radii of the charts from 10 to 100 and the degrees of temperatures of the dry,

"bulb thermometer are marked upon the outermost are of the chart. When the temperatures at the two thermometers are the same, the relative humidity will be 100 and the air will be saturated. The temperature shown by the dry 3 bulb thermometer can'neverbe less than that shown by the wet bulb thermometer because when the temperatures are the same the relative humidity will be 100, the air being saturated, and consequently it will not be possible for any evaporation to take place at the wet bulb thermometer. The relative humidity at any given temperature will be indicated at the point where the line running from the center of the chart to the periphery thereof and indicating the dry bulb temperature is crossed by a line representing wet bulb temperature.

In the mechanism illustrated in the drawings a disc or circular plate 15 is fixed to one end of the cam 3 and projects radially from the shaft 5 beyond the range of the cam. Disposed parallel with the shaft is a cylinder or cylindrical body 16 having a cam groove 17 formed in its circumferential surface, and disposed between the shaft 4 and this cylindrical body is a guide rod 18 which is stationary and upon which is mounted a slide 19 having on one side a pair of spaced ears or lips 20 which receive the periphery of the plate 15 between them. At the opposite side of the slide is a finger or pin 21 which 5 engages slidably in the cam groove 1'7 so that as the cylindrical body 16is rotated the slide will be caused to move along the guide rod 18 and thereby shift the plate 15 and the controlling cam 3 along the shaft 4. The cylindrical body. 11

16 is fixed upon a shaft 22 mounted in suitable bearings 23 which may be also utilized as supports for the guide rod 18 and upon one end of the shaft is a segmental gear 24 meshing with a segmental gear 25, said segmental gear 25 being pivotally mounted upon the bearing support 23 and connected with a crank arm 26 which is connected by a link 27 with a Bourdon tube 28, the Bourdon tube 28 being connected with the wet bulb thermometer tube 2 through a capillary tube 29. It will now be understood that when the temperature at the wet bulb thermometer rises, the mercury in said thermometer will expand through the capillary tube 29 and the Bourdon tube 28 and tend to straighten the latter so that the shaft 22 will be rocked through the gearing shown and described and the slide 19 will be caused to move along the guide rod 18, the controlling cam 3 following the movement and shifting longitudinally of the shaft 4. The controlling cam 3 will thus be responsive to both thermometers and its sliding and turning movements may occur simultaneously and to different extents according to the variations in the temperatures.

Slidably mounted in suitable supports is a bar or rod 30 having a rack 31 on one side and meshing with said rack is a gear 32 which is carried by a vertical shaft or rocking post 33 mounted in suitable bearings at one side of the rod 30. The rod 30 has one end bearing constantly against the controlling cam 3, as shown at 36, and a coil spring 34 is provided and acts constantly upon the gear 32 so as to maintain the engagement between the cam and the end of the rod. The end of the rod or bar 30 presented to the cam is offset, as shown at 35, so as to be centralized with respect to the shaft or post 33. The shaft or rocking post 33 is extended above the gear 32 and a pointer 37 is fixed to the upper end of the post, said pointer extending over the cam 3 and terminating above an arcuate scale 38 to play above the scale and come to rest when the cam is at rest over the proper graduation of the scale. Thezdegrees upon the scale are calibrated for degrees of relative humidity and the position of the pointer will be determined by the position of the controlling cam which in turn is set according to the temperatures at the dry and wet bulb thermometers.

In Figures 4, 5 and 6 I have shown a somewhat diiferent mechanism for transmitting the by a link or connecting bar 42 with a similar radial arm or crank 43. The arm or crank 43 is fixed upon a shaft 44 which carries a segmental gear 45 disposed in a vertical plane and meshing with a similar gear 46 disposed at an angle thereto, the gear 46 beingfixed to a vertical shaft or pivot 47 upon the upper end of which the pointer 48 is secured. The pointer 48 corresponds in all respects to the pointer 37 and plays over a scale 49 which corresponds to the scale 38. A spring 50 is provided to act upon the gear 45 and connected parts so as to hold the finger 40 constantly in contact with the surface of the controlling cam.

From the foregoing description taken in connection with the accompanying drawings it will be seen that I have provided a mechanism whereby the relative humidity of the air may be determined at a glance at any time without requiring mental calculations or the consultation of any other data, no calculation being required. The controlling cam 3 will respond instantly to the variations in temperature at the two thermometers and will consequently set the pointer promptly at the proper graduation of the scale to show the humidity. The details of the operating mechanism may be varied widely without departing from the spirit or scope of my invention provided there is retained a controlling cam which operates in two directions or in two planes and is actuated directly by the wet and dry bulb thermometers to give a direct reading indicating the humidity of the air. The illustrated mechanism is compact and free from complicated arrangement or constructions which are apt to get out of order and require constant repairing.

Having described the invention, I claim:

1. A hygrometer including wet and dry bulb thermometers, a shaft mounted in spaced relation to the thermometers, a scale arranged adjacent the shaft and indicating degrees of humidity, a cam mounted upon the shaft and slidable along the same but constrained to rotate therewith, a pointer playing over the scale, a slide in contact with the'cam and geared to the pointer whereby the position of the pointer will be determined by the movements of the cam, gearing at one end of the shaft to rotate the same, a Bourdon tube connected to said gearing, a capillary tube extending from the dry bulb thermometer to the Bourdon tube for operating said gearing whereby the cam will be caused to rotate responsive to variations of temperature at the dry bulb thermometer, and means controlled by the variations at the wet bulb thermometer to effect sliding movement of the cam.

2. A hygrometer including wet and dry bulb 125 thermometers, a shaft mounted in spaced relation to the thermometers, a scale disposed adjacent the shaft to indicate degrees of humidity,

a cam mounted upon the shaft for sliding movement and constrained to rotate therewith, a 130 pointer playing over the scale and controlled by said cam, means whereby variations in temperature at the dry bulb thermometer will effect rocking of the cam, a cam cylinder disposed parallel with the shaft, means whereby variations in 135 temperature at the wet bulb thermometer will rock said cam cylinder, a slide engaged in said cylinder for movement from end to endthereof, and means whereby the movement of said slide will effect sliding movement of the controlling 140 cam.

1 FRANCIS B. FOSTER. 

